The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Metal-Organic Frameworks (MOFs) are a class of promising porous materials having tuneable functionality, large pore sizes and the highest known surface areas. These characteristics are of high interest for a myriad of industrial applications such as gas storage, gas separation, drug delivery and catalysis. However, to date the cost of these materials has remained prohibitively high, thereby restricting the ability of these materials to make a significant impact on prospective markets or technologies. Only seven MOFs out of the thousands of MOFS described in academic literature are commercially available, with that availability limited to small quantities (grams).
An important requirement for accessing the potential applications of MOFs is the ability to routinely synthesise MOF materials in large quantities (kg scale or higher) at an economic price point. Such a process needs to be a versatile, efficient and scalable synthesis that is able to produce MOFs in large quantities in order to introduce these materials to real world applications.
However, traditional laboratory routes such as the classical solvothermal synthesis are difficult to scale up due to the extended reaction times (˜24 hours) and low quality material yield. Furthermore, a wide variety of available synthetic synthesis methods have a singular nature providing an inherent inflexibility for any prospective production process.
Large-scale process post synthesis steps such as cleaning, separation and activation can also be crucial for cost-effective production of high quality MOF material.
There are a number of known technologies for solid-liquid separation including centrifuges, cyclones, electrostatic precipitators, settling chambers, classifiers or filters, and evaporation. However, the small size of the MOF particles, their low concentration in the solvent, as well as their density approaching that of the solvent (due to the high porosity), makes separation unfeasible, inefficient or expensive at an industrial scale using most conventional methods.
Sedimentation- or tubular-type centrifuges are known to process solids as small as 100 nm, while wet electrostatic precipitators can also handle particles above 50 nm with 98% efficiency and greater than 100 nm with 95% efficiency. Yet, a high capital investment is generally required and this type of equipment also has generally high overall power consumption.
Liquid-solid filters can process particles as small as 500 nm, when operated under pressure (typically 2-15 bar for continuous rotary drum, or 3 to 70 bar for batch), or when using cartridge or sand (packed bed) filters (batch operation). However, filters requiring a high pressure drop across the separation stage are subject to fouling over time while pressurised rotary drum filters have a very high capital cost.
It would therefore be desirable to provide a new and/or improved method of separating and/or purifying a MOF in solution from contaminants, without destroying the integrity of the porous MOF.